第6章 LabVIEW面向对象程序设计

《面向对象程序设计》教案一、教案简介本教案旨在帮助学生掌握面向对象程序设计的基本概念、原理和方法，培养学生的编程能力和软件开发思维。

通过本课程的学习，学生将能够熟练运用面向对象的编程语言，如Java或C++，进行软件开发和设计。

二、教学目标1. 了解面向对象程序设计的基本概念，如类、对象、封装、继承和多态等。

2. 掌握面向对象程序设计的基本原则，如单一职责原则、开闭原则、里氏替换原则等。

3. 学会使用面向对象的编程语言进行程序设计和开发。

4. 培养学生的软件开发思维和团队协作能力。

三、教学内容1. 面向对象程序设计的基本概念1.1 类与对象1.2 封装1.3 继承1.4 多态2. 面向对象程序设计的基本原则2.1 单一职责原则2.2 开闭原则2.3 里氏替换原则2.4 接口隔离原则2.5 依赖倒置原则3. 面向对象的编程语言3.1 Java3.2 C++4. 面向对象的设计模式4.1 创建型模式4.2 结构型模式4.3 行为型模式四、教学方法1. 讲授法：讲解面向对象程序设计的基本概念、原理和编程方法。

2. 案例分析法：分析实际项目中的面向对象设计案例，让学生理解并掌握面向对象的设计思想。

3. 实践操作法：让学生通过编写代码，亲身体验面向对象程序设计的流程和方法。

4. 小组讨论法：分组进行讨论，培养学生的团队协作能力和解决问题的能力。

五、教学评价1. 课堂参与度：评估学生在课堂上的发言和提问情况，了解学生的学习兴趣和积极性。

2. 课后作业：布置相关的编程作业，检查学生对面向对象程序设计知识的掌握程度。

3. 项目实践：评估学生在团队项目中的表现，包括代码质量、设计思路和团队协作能力。

4. 期末考试：全面测试学生对面向对象程序设计知识的掌握情况。

六、教学资源1. 教材：推荐《Java面向对象程序设计》、《C++ Primer》等经典教材。

2. 在线资源：提供相关的在线教程、视频课程和编程练习平台，如慕课网、Coursera、LeetCode等。

LabVIEW中的面向对象编程技术在LabVIEW中的面向对象编程技术LabVIEW是一种基于图形化编程的工程软件。

它以图形化的方法创建程序，主要用于测试、测量和控制应用。

除了其强大的数据采集和处理能力外，LabVIEW还提供了面向对象编程（Object-Oriented Programming，简称OOP）技术，使得开发人员能够更加高效和灵活地设计和实现复杂的应用。

本文将介绍LabVIEW中的面向对象编程技术及其应用。

一、面向对象编程技术简介面向对象编程是一种软件开发方法，它以对象为基本单位，通过封装、继承和多态等特性，将程序的数据和对数据的操作进行有机的结合，使得程序的设计更加模块化、可复用和易于维护。

在LabVIEW中，面向对象编程技术被应用于虚拟仪器对象（Virtual Instrument Object，简称VI）的设计和开发。

VI是LabVIEW 程序的基本单位，通过面向对象的思想，可以将VI的功能、数据和界面封装成一个独立的对象，从而实现对其进行灵活的组合和重用。

二、LabVIEW中的面向对象编程1. 类和对象在LabVIEW中，类是面向对象编程的基本概念。

类定义了对象的属性和方法。

对象是类的实例，每个对象都有自己的属性值和方法。

2. 封装封装是面向对象编程的核心思想之一，它可以隐藏对象的实现细节，使得对象的使用者只需关注对象的接口。

在LabVIEW中，封装可以通过访问控制功能来实现。

例如，可以将某些属性设置为只读或只写，以限制对属性的访问权限。

此外，还可以使用属性节点来对属性进行封装，只允许通过特定方法对属性进行访问。

3. 继承继承是面向对象编程的另一个核心概念，它可以通过扩展已有的类来创建新的类，从而实现代码的重用和扩展。

在LabVIEW中，可以通过创建派生类来实现继承。

派生类继承了基类的属性和方法，并可以在此基础上进行扩展和修改。

通过继承，可以实现对现有功能的改进和功能的复用。

LabVIEW的面向对象编程指南LabVIEW是一款强大而灵活的图形化编程语言，广泛应用于数据采集、信号处理、测量与控制等领域。

而实现这些功能的关键就是面向对象编程（OOP）。

本文将深入探讨LabVIEW中的面向对象编程，为您提供一份指南，助您在LabVIEW中灵活运用面向对象编程技术。

1. 面向对象编程的基本概念面向对象编程是一种将现实世界的事物抽象成“对象”，并通过定义对象的属性和行为来实现系统开发的编程方法。

在LabVIEW中，对象是基于类（Class）的概念进行创建和使用的，每个类都有自己的数据和方法。

2. 类和对象的创建在LabVIEW中，类是创建对象的模板，是一种用户自定义的数据类型。

通过定义类的数据成员（属性）和方法（行为），可以实例化一个对象。

通过面向对象编程，可以封装数据和方法，实现代码的可重用性和扩展性。

3. 封装和继承封装是面向对象编程的核心概念之一。

它指的是将数据和方法封装在类内部，通过接口提供对外访问。

在LabVIEW中，可以使用“公共接口”来定义类的公共方法和属性，使得其他开发者可以通过对象调用这些方法和属性。

继承是指一个类可以继承另一个类的属性和方法，可以减少代码的重复编写，提高代码的复用性。

4. 多态性多态性是面向对象编程的另一个重要概念。

它可以通过定义一个通用的接口，让不同类的对象都可以实现该接口，并根据对象的不同实现调用不同的方法。

在LabVIEW中，可以使用动态调度方法，通过接口调用对象的方法，实现多态性的效果。

5. 事件驱动编程除了封装、继承和多态性，LabVIEW中的面向对象编程还支持事件驱动编程。

通过定义事件和事件处理程序，可以实现对象间的交互和通信。

当事件发生时，LabVIEW将自动调用相应的事件处理程序，对事件进行响应和处理，提高系统的灵活性和响应性。

6. 错误处理和调试在面向对象编程中，良好的错误处理和调试技术是不可或缺的。

LabVIEW提供了一系列的错误处理工具，如错误处理节点和自定义错误码等，可以帮助开发者在程序运行过程中及时捕获并处理错误。

LabVOOP Design Patterns (version 1.0) Stephen Mercer, LabVIEW R&D, National InstrumentsTable of ContentsIntroductionThe PatternsSingletonFactoryHierarchy CompositionDelegationAggregationSpecificationChannelingVisitorConclusionIntroductionWhen talking about computer programming, a design pattern is a standard correct way to organize your code. When trying to achieve some particular result, you look to the standard design patterns first to see if a solution already exists. This sounds a lot like an algorithm. An algorithm is a specific sequence of steps to take to calculate some result from a set of data. Generally algorithms can be written once in any given programming language and then reused over and over again. Design patterns are rewritten over and over again. For example, in house cleaning, consider this algorithm for vacuuming a carpet: “Start in one corner, walk horizontally across the floor, then move to the side and continue making adjacent parallel stripes until the whole floor is vacuumed.” Compare this with the design pattern for cleaning a room: “Start cleaning at the ceiling and generally work your way down so that dirt and dust from above settle on the still unclean areas below.” Design patterns are less specific than algorithms. You use the patterns as a starting point when writing the specific algorithm.Every language develops its own design patterns. LabVIEW has patterns such as “Consumer/Producer Loops” or “Queued State Machine.” These are not particular VIs. Many VIs are implementations of queued state machines. When a LabVIEW programmer describes a problem, another programmer may answer back, “Oh. You need a queued state machine to solve that problem.” Starting in LabVIEW 7.0, LabVIEW has had VI Templates for many LabVIEW design patterns available through the File>>New… dialog. With the release of LabVIEW Object-Oriented Programming, we need to find the new patterns that arise when objects mix with dataflow.The seminal text on design patterns appeared in 1995: Design Patterns by Gamma, Helm, Johnson and Vlissides. This text is colloquially known as “the Gang of Four book.” This text focused on object-oriented design patterns, specifically those that could be implemented using C++. Many of those patterns are predicated on a by-reference model for objects. As such they apply very well to classes made with the GOOP Toolkit (or any of the several other GOOP implementations for LabVIEW). LabVIEW classes, added in LV8.2, use by-value syntax in order to be dataflow safe. This means that the known patterns of object-oriented programming must be adapted, and new patterns must be identified. This document describes the LabVOOP-specific patterns I have identified thus far.This document is not on NI’s DevZone as I do not wish to give an official imprimatur to these yet. The descriptions and methods of implementation may not be as optimal. I am posting these as a common LabVIEW user, not as a member of LabVIEW’s R&D team.– Stephen Mercer Reference:Design Patterns Gamma, Erich, et al. 1995.Addison Wesley Longman, Inc.Singleton Pattern(adapted from Gang of Four’s Singleton pattern)IntentGuarantee that a given class has only a single instance in memory, that no second instance can ever be created, and that all method calls refer to this single instance.MotivationWhen you create a class, sometimes it is advantageous to guarantee that a program always refers to the same global instance of the class. Perhaps the class represents a database. It would be unfortunate if some section of code accidentally instantiated its own database and thus failed to update the global database. Creating a global means all VIs can access the data. But it does not mean that all VIs will access the global. This pattern describes a framework of classes that guarantee that single instance of data.ImplementationSee/SingletonPattern.zip(An example of this pattern shipped with LV8.2, but that example is flawed, a problem I did not realize before we released: <labview>\examples\lvoop\SingletonPattern\Design Pattern.lvproj )In this implementation, we seek to guarantee a single instance of Data.lvclass. We achieve this by putting Data.lvclass into an owning library, Singleton.lvlib, and making the class private. Now no VI outside the class can ever drop the class as a control, constant or indicator, so we guarantee that all operations are limited to this library. Callers can use Singleton.lvlib:Checkout.vi to get the current value of the data, modify it using any of the operations defined by Singleton.lvlib and then set the new value with Singleton.lvlib:Checkin.vi. The public functions are the same functions that would normally be on the class itself. They are moved to the library so that the functionality is exposed without allowing the class itself to be dropped. Checkin.vi and Checkout.vi use a single-element queue to guarantee only one copy in memory at a time. While the element is checked out to be modified by some routine, no other operation can proceed, thus guaranteeing serial access to the data. Editorial CommentsI do not like the implementation that shipped with LV8.2. In the time since LV8.2 released, I have found better ideas. This “post-release discovery” is one reason why more design patterns are not included with the shipping product. LabVOOP is too new, and many of the patterns identified during development may be found faulty when exposed to a wider audience (i.e. real customers). So I’m making this implementation available.The only hole in the above solution that I can find is VI Server. VI Server could get a reference to the Front Panel controls of Singleton’s member VIs and use the Value property to effectively manipulate a different instance of the class than the one in the queue. Would using Subroutine Priority prevent VI Server access? I think so, but that seems like a pretty odd way to fix these VIs. The fix may not be that necessary – I doubt that many people are going to attempt such a hack on the class. Anyone trying it is already aware that they’re working against the design of the class and may break components that depend upon the singleton nature.Factory Pattern(adapted from Gang of Four’s Factory pattern)IntentProvide a way to initialize the value on a parent wire with data from many different child classes based on some input value, such as a selector ring value, enum, or string input. This may include dynamically loading new child classes into memory. Ideally new child classes can be created and used without editing the framework. MotivationData comes from many sources – user interface, network connection, hardware – in a raw form. This data frequently comes in types, and the data is to be handled generically but each type has a specific behavior at the core of the handling. Such a problem cries out for the use of classes and dynamic dispatching. We want to write an algorithm around some common parent type and then let dynamic dispatching choose the correct subVI implementation for the parts of the algorithm that are type specific. The hard part is in initializing the right class from the input data.ImplementationAn example of this pattern was made available by Christina Rogers in her refactoring of the Getting Started Window in the Init From XML methods. Information about this example is available here:/2006/08/object-oriented-getting-started-window.htmlThe general idea is this: Use your data to identify which class you are interested and get the name and/or path to that class’ file. Then use the Application Properties to get access to that class. Suppose we name our parent class Generic Plugin.lvclass. All of our data will be wrapped by specific child types of Generic Plugin. After we have chosen the path to the child class, we proceed as follows:1.Open reference to the .lvclass file on disk. This returns a LVClassLibrary refnum.2.Get the default instance of the class.3.Cast the LabVIEW Object that gets returned to your plug-in data type.From there you would wire the chosen class instance to an Init method of the class which would take your data as an input. The advantage of this system is that the child class is only loaded into memory if someone actually wants to instantiate that child. If you have a great many possible types of data, this can save on memory and load time for your application. The name of this pattern comes from the fact that a single VI serves as a factory to produce all the myriad child types.Editorial CommentsThis implementation does not work in the run time engine because the LVClass refnum does not exist in the runtime engine. Without this, a much less elegant solution must be used. Instead of identifying the path to the class, use your data to pick an enum value, and wire that enum to a case structure. Each frame of the case structure should have a constant of the specific child class. This alternative implementation does not do dynamic loading and requires that all child classes be known and in memory when the VI loads. It further means editing the factory each time a new child class is created.Hierarchy Composition Pattern(adapted from Gang of Four’s Composite pattern)IntentTo represent a single object as a tree of smaller instances of that same object type. Useful for images (an image is made of a set of subimages), file systems (directory contains both files and other directories) and other systems where there is a common aspect to both the whole object and its parts.Motivation“Composition” refers simply to using one class as member data of another class. One class is thus “composed” of another class. The Hierarchy Composition pattern is specifically for times when you are making a class that is going to be composed of smaller instances of itself.ImplementationAn example of this pattern shipped with LV8.2. See<labview>\examples\lvoop\Graphics\Graphics.lvprojThis example includes a class hierarchy for Graphic.lvclass, as shown in the image.A graphic is simply something that can be drawn. Graphic defines a method Draw.vi,which can be overridden by children. There are three children of Graphic. The first twoare straightforward implementations: Point.lvclass and Line.lvclass. Each of these twohave coordinate data as their member data, and implement Draw.vi accordingly. Thethird class, however, is Collection.lvclass. Collection has as its private data an array ofGraphics. That is, Collection, which is itself a Graphic, contains other Graphics. It’simplementation of Draw is to loop over that array and call Draw for each containedelement. The demo shows how a Collection graphic can be built up from individualpoints and lines.You could continue this, adding a Collection inside a Collection, nesting them to createmore complex Graphics.The difficulty arises when trying to call Draw for a Collection that contains another Collection. This is a recursive call to Collection.lvclass:Draw.vi. LabVIEW does not support recursion and will abort the VI when the recursion is attempted at runtime. There are ways around this barrier. Exploration of the various pros and cons of the workarounds has been proceeding on the LAVA Forums:/index.php?showtopic=3830Delegation PatternIntentTo have two independent classes share common functionality without putting that functionality into a common parent class.MotivationGood object-oriented design requires each class to focus on its assigned task. A class shouldn’t have member VIs unrelated to its task. If you have two classes that have some shared functionality, the usual solution is to create a parent class that both of them inherit from. Sometimes, however, you already have a class hierarchy created and a new feature comes along. The new functionality needs to be added to two existing classes that either do not have a common ancestor or do have a common ancestor but that ancestor is several generations up and not every descendent of that ancestor should have the new functionality. In some languages you might try multiple inheritance. But even in languages that support multiple inheritance, delegation is generally a better solution.This pattern applies best when you have a dynamic VI inherited from some ancestor and two descendent classes want to override that dynamic VI with exactly the same implementation. Delegation helps you avoid writing the implementation twice, once for each of the two classes.ImplementationAn example of this pattern was made available by Christina Rogers in her refactoring of the Getting Started Window in creation of her Project Wizard class. Information about this example is available here:/2006/08/object-oriented-getting-started-window.htmlThe general idea is this: Create a third class that has the new functionality. The new class is frequently something like “Function Helper” or “Function Assistant,” where “Function” is whatever functionality is to be delegated. Give that class all the data fields necessary to carry out the new functionality. Then add that third class as a data member to the two classes that need to share the functionality.The two descendent classes override the ancestor’s dynamic VI. But they only put in a bit of code necessary to call the exact same method on their data member of the helper class. The actual work is entirely in that method of the helper class. Now there is only a single instance of the code, which makes bug fixing easier. The two descendent classes have delegated the work to a third class. Thus the name of this pattern.Editorial CommentsThis pattern is not listed explicitly in the Gang of Four text. The idea occurs as an aspect of several other patterns. I think it is useful enough to warrant specific attention.IntentTo treat an array of objects as a single object.MotivationAn array nicely collects data together into an indexable list. But there are many primitives that operate on an array: Build Array, Remove From Array, etc. There are times when you want an array to guarantee certain properties, such as:•an array that guarantees that no duplicates are ever inserted•an array that is always sorted•an array that doesn’t allow removing elementsThis pattern creates a class that lets you treat an array of another class as a single object.ImplementationNo examples of this pattern are publicly available yet. Here is a summary of the pattern:Suppose you have Data.lvclass. Now you create ArrayOfData.lvclass. In ArrayOfData’s private data cluster, you add an array of Data. The only operations that can be performed on this array are those that you add to ArrayOfData. To guarantee no duplicates, write Insert Element.vi such that it checks the array for existing values before doing the insert. If you need to make sure the data stays sorted, you can write Insert Element.vi such that it inserts data at the correct position. Whatever functionality you supply – or leave out, as in the case of an array that does not allow removing elements – defines what can happen to the array.The new class represents an aggregation of many instances of another class. Thus the name of this pattern. Editorial CommentThis is an easy pattern to understand, and it is easy to think of the implementation on your own. Not all the patterns are complex systems. Sometimes pointing out the obvious is useful. When planning a new application, you may look at a list of patterns to consider what the best design would be. Having these so-called “obvious” patterns in the list helps remind you that you ought to use them. Because as easy as this pattern is, it is easier just to have a raw array running around on your diagram (you don’t have to write a bunch of accessor VIs to duplicate the functionality already found on certain primitives). There are times when you’ll choose to do that. But as your code gets more complicated over time, you may find yourself wishing that you had wrapped the array up so that you could guarantee certain characteristics.IntentTo have different functionality for a class depending upon some value of the class without updating case structures throughout your VI hierarchy when you add another value.MotivationYour data has some field – perhaps an enum, perhaps a string, perhaps something more complex – and you have a case structure that cases out on that field to decide which of several actions to perform. The data in this field is constant (once you have initialized the class this field never changes). When you find yourself creating a lot of these case structures, or, worse, updating a lot of these structures to add a new case, you should remember this pattern.ImplementationExamples of this pattern occur in just about every shipping example.If the data is constant from the time the class is initialized onward, then you should strongly consider creating a set of child classes. The data in that field is unnecessary data – stop hauling it around the diagram. A class knows its data type. If you need that value, you can get it from some static VI on the class that just returns a constant. Further, those case structures can now be replaced with dynamic subVI calls. For every distinct case structure, create a new dynamic VI on the parent class and put the code that used to be in each frame of the case structure in one of the children’s override VIs. Now when you add a new case, there are no case structures to update. So instead of one monolith class with an enum type, you now have many more specific classes. Thus the name of this pattern.This pattern is frequently used in conjunction with the Factory pattern.Editorial CommentLike the Aggregation pattern, this is an “obvious” pattern. But it is easy to overlook the fact that a piece of data never changes. If data never changes, that data is effectively part of the data type. Clusters that carry around the name of their data or a string representing the source of the data cry out for application of this pattern. This pattern is basically the central use case for class inheritance and dynamic dispatching. It simplifies many very complex VIs and clusters into manageable chunks by giving an easy way to break up the functionality of the case structure across multiple VIs. This pattern is the first one that a new user of object-orientation should learn, and generally the first one to consider when refactoring existing applications.Channeling PatternIntentTo provide a guaranteed pre-processing/post-processing around some dynamic central functionality.MotivationYou have a class hierarchy. And you have some algorithm that you want to implement on the parent class. There is a core step of the algorithm that needs to be dynamic so that each child class can provide its own behavior. But it is unsafe to call that step directly – you want a class interface that guarantees the step is only called from the algorithm VI.ImplementationNo examples of this pattern are publicly available yet. Here is a summary of the pattern:The parent class has the VI that implements the algorithm. Make the algorithm VI a static VI (no dynamic inputs). That way the child classes cannot override the algorithm itself and thereby avoid calling the pre-processing/post-processing. Make the dynamic step of the algorithm a dynamic VI that the child classes can override and make the dynamic VI be protected in the parent class. This forces all the children to use protected scope for their override VIs. No VI outside the class hierarchy will be able to call the dynamic VIs directly. This pattern does not prevent child classes from calling the step on themselves or other child classes without going through the algorithm. It does make sure that all the VIs outside the class hierarchy always go through the algorithm VI.The name of this pattern refers to the control of the flow of data – the data is channeled through the static VI to get to the dynamic VIs.Editorial CommentA customer asked me why all member VIs in classes aren’t dynamic. The performance overhead of dynamic VIs is pretty small (and constant no matter how deep the class hierarchy or how many dynamic VIs there are on the class) such that it made sense to the customer to make all the VIs dynamic and only make static VIs if a performance problem actually arose. That would give maximum flexibility to the class. This pattern is one of several reasons not to make everything dynamic. If the algorithm itself were dynamic, child classes might decide to override the algorithm and skip the pre/post processing. This pattern is particularly useful for large programming teams where you might not know all the developers, or where child classes will be implemented by third parties. It lets the original author put compiler-enforceable guidelines into the code so that future programmers do not unwittingly write VIs that will create issues for the architecture.Visitor Pattern(adapted from Gang of Four’s Visitor pattern)IntentTo write a traversal algorithm of a set of data such that the traversal can be reused for many different operations.MotivationSuppose I have an array of integers. I need a function that will calculate the sum of those integers (ignore, for the sake of argument, the fact that there’s a primitive to do this). I drop a For loop and iterate over every value, adding each element to a running total in an uninitialized shift register. The value in the shift register when the loop finishes is my sum.Now suppose I want to find the product of those integers. I write the same For loop and shift register, only instead of the Add primitive, I use Multiply. Everything about these two VIs is exactly the same except for the core action. How can I avoid duplicating so much code?Dynamic dispatching does not immediately help in this case – I do not have any child types on any of the wires that I can dispatch on. I could make my traversal VI have a VI Reference input. Then, instead of calling a primitive, I could have a Call By Reference node. The VI that I pass in would have either the Add or Multiply primitive.This is helpful, but only works if my two VIs have exactly the same connector pane. What if I need other information, other parameters, to do the job in that Call By Reference node?ImplementationAn implementation of this pattern is available here:/LV2OO_Style_Global_v1.0.zipInstead of taking in a VI Reference, the traverse VI takes in an object of class Action. This is a class that you define. Create one child class of Action for each specific action you want to do during the traversal. Then instead of a Call By Reference node, call the Do Action.vi method. This will dynamically dispatch to the correct implementation. The Action object can have all sorts of data inside it that can augment the operation at hand. You can implement as many new Action children as you want without ever having to change your original traversal framework.The traversal VI can get very complicated, far beyond the simple For loop over an array that I mention here. As the traversal walks over a data set, the Action object “visits” each piece of data and updates itself. Thus the name of this pattern. Your visitor can collect a summary of information about the pieces of data (such as the sum and product calculations), or it might search for a particular value, or it might even modify the data as it visits (divide each value in the array by 2). The traversal works just as well in all of these cases.Editorial CommentI am tired of writing LV2-style globals. These globals are great – very dataflow efficient, very easy to understand. But you have to duplicate the VI every time you want to support a different data type. I figured there had to be a better way. I’ve been thinking about this implementation for a while. It may not be optimal, but I think it is an excellent starting point. Imagine… the possibility of never writing another LV2-style global VI ever again, because you could just reuse one and give it the particular action that you want. A whole new flavor of über-geek nirvana!ConclusionThose are the design patterns thus far. I hope to update the list as time goes by, both with more patterns and with better examples for the existing patterns. Pay attention to the code you write – when you find yourself following the same routine over and over, try giving a name to the pattern. See if you can clearly identify when it is useful and how best to do it.Exploration of these patterns helps us design better code. Using the patterns is using the learning of previous developers who have already found good solutions. In studying the patterns, we can learn what good code “feels” like, and we are then more aware when we create an unmaintainable hack in our own programs.When we follow the standard designs it helps others looking at our code understand what they’re looking at. If a programmer knows the general pattern being used, he or she can ignore the framework and focus on the non-standard pieces. Those are the points are where the program is doing its real work. It is akin to looking at a painting in a museum – the painting is the interesting part. The picture frame and the wall are just there to hold up the art. If the frame or wall are too decorative, they pull the focus.I do not talk about any anti-patterns in this document. Anti-patterns are common attempts that look like good ideas but have some generally subtle problem that will arise late in development. Some anti-patterns in other languages are sufficiently detectable that a compiler could even be taught to recognize them and report an error. Perhaps these exist in LabVIEW. We should be cataloguing these as well.For those who chose object designs,we want the world of wire and nodeto morph naturallyinto a world of class and method.– LabVOOP。

LabVIEW 面向对象程序设计的简介LabVIEW 的数据流驱动模式，与面向过程的编程思想有些类似。

它们都是把程序看成是一组过程或功能的集合，LabVIEW 利用数据流控制这些功能执行的顺序。

由于开发者可以随意的修改、调用这些功能模块，在程序开发的后段，模块之间的划分会变得模糊，依赖关系也变得无序。

这种方式就不再适合大型程序的开发。

面向对象的编程思想是专为解决这个问题提出来的。

面向对象的编程思想大大提高了编程时的灵活性和可维护性。

现在的大型程序中几乎没有不基于面向对象编程思想的。

LabVIEW 为了适应这一趋势，也从8.2 版本开始引入了面向对象程序设计的思想。

面向对象有三大特征：封装、继承和多态。

封装是把高度相关的一组数据和方法组织在一起，形成一个相对独立的类。

外部程序只能通过严格定义好的接口访问类所允许公开的数据和方法;而对于不需与外部发生联系的数据和方法，类会把他们隐藏和保护起来。

这样就避免了编程过程中，函数模块常常被到处滥用以至于难以维护的弊病。

(假如，我们的程序是模拟多只小狗的日常生活的。

在设计程序时，就可以把他们抽象归为“狗”类。

这个类包括了一些属性，如年龄、皮毛颜色、名字等等;还可以包含一些方法，即狗的行为，比如进食、移动、叫等。

)初一看LabVIEW 中的Class 就会发现它很像Cluster，或许它就是在Cluster 基础上发展来的。

C++ 中的Class 也是在Struct 的基础上发展来的，而且，在C++ 中，除了函数默认的权限不同，Class 和Struct 是等效的。

在LabVIEW 中，二者还是截然分开的，Cluster 中只有数据，Class 中除了数据，还可以有方法。

C++ 类中的成员变量可以是私有，也可以是共有;为了安全起见，LabVIEW 中所有的数据都是私有的，必须通过公有的VI才能访问这些数据。

C++ 的类拥有构造函数和析构函数;LabVIEW 的类没有这两个方法。

LabVIEW编程中的面向对象设计与开发方法LabVIEW是一种流程式编程语言，广泛应用于数据采集、仪器控制以及测试和测量领域。

面向对象设计和开发方法在LabVIEW编程中起着重要的作用，可以提高代码的可维护性和重用性。

本文将探讨LabVIEW编程中的面向对象设计与开发方法。

一、面向对象编程简介面向对象编程（Object-Oriented Programming，OOP）是一种程序设计范型，主要思想是将现实世界的概念抽象成为对象，并通过对象之间的交互来实现程序的功能。

面向对象编程具有封装、继承和多态等特性，能够提高代码的可读性和可维护性。

二、LabVIEW中的面向对象设计原则在LabVIEW中，可以通过使用面向对象的设计原则来提高程序的可维护性和灵活性。

1. 封装性（Encapsulation）：将数据和操作封装在对象中，通过公共接口进行访问。

在LabVIEW中，可以使用类（Class）来实现封装性，将数据和方法封装在类中。

2. 继承性（Inheritance）：通过继承机制，可以实现代码的重用，并且方便对代码进行扩展。

在LabVIEW中，可以使用继承关系来实现类之间的关联。

3. 多态性（Polymorphism）：通过多态机制，可以实现接口的统一，提高代码的灵活性。

在LabVIEW中，可以使用虚方法（Virtual Method）和动态派生（Dynamic Dispatch）来实现多态性。

三、LabVIEW中的面向对象开发方法1. 创建类（Class）：在LabVIEW中，可以通过面向对象的方式创建类。

首先，需要创建一个新的面板，并在控件栏中选择"新增类"。

然后，可以根据需要添加属性和方法，并设置访问权限。

2. 定义类的继承关系：在LabVIEW中，可以通过继承关系来实现代码的重用。

在创建类时，可以选择继承已有的类。

通过继承，子类可以继承父类的属性和方法，并根据需要进行扩展。

labview面向对象编程项目实例LabVIEW面向对象编程（Object-Oriented Programming, OOP）是一种在LabVIEW中使用面向对象设计原则和技术进行软件开发的方法。

本文将介绍一个基于LabVIEW的面向对象编程项目实例，以帮助读者更好地理解和应用这种编程方法。

标题：LabVIEW面向对象编程项目实例引言：在LabVIEW中，面向对象编程提供了一种高效且可维护的软件开发方式。

通过将软件系统划分为多个对象，并通过对象之间的交互实现功能，可以提高代码的可重用性和可扩展性。

本文将以一个简单的实例介绍如何在LabVIEW中利用面向对象编程进行软件开发。

一、项目背景和需求假设我们需要开发一个简单的学生管理系统，该系统需要实现以下功能：1. 添加学生信息（包括姓名、年龄和成绩）；2. 查询学生信息；3. 统计学生人数；4. 计算学生平均成绩。

二、面向对象设计为了实现以上功能，我们可以设计以下对象：1. 学生类（Student）：包含学生姓名、年龄和成绩等属性，以及添加学生信息和查询学生信息的方法。

2. 学生管理类（StudentManager）：包含学生列表、添加学生信息、查询学生信息、统计学生人数和计算学生平均成绩等方法。

三、LabVIEW面向对象编程实现1. 创建学生类我们可以创建一个包含学生属性和方法的学生类。

在LabVIEW中，可以使用类定义来表示一个类。

学生类可以包含以下属性：- 姓名：字符串类型- 年龄：整数类型- 成绩：浮点数类型学生类可以包含以下方法：- 添加学生信息：输入学生属性，将学生信息添加到学生列表中；- 查询学生信息：输入学生姓名，返回对应的学生信息。

2. 创建学生管理类学生管理类可以包含以下属性：- 学生列表：用于存储学生对象的列表。

学生管理类可以包含以下方法：- 添加学生信息：输入学生属性，创建学生对象并添加到学生列表中；- 查询学生信息：输入学生姓名，遍历学生列表，找到对应的学生对象并返回其信息；- 统计学生人数：返回学生列表的长度，即学生人数；- 计算学生平均成绩：遍历学生列表，累加所有学生的成绩并计算平均值。

适配器模式适配器是常见的硬件概念，比如我们常用的USB转RS232适配器。

我们乊所以采用适配器，主要是由于以下原因：一、原有硬件设备已经存在，新的连接设备不存在和旧设备一致的接口。

二、新的设备需要连接很多不同接口的设备，需要构建一个统一的接口。

OOP适配器模式借用了硬件适配器的概念。

软件的升级换代是非常常见的，对于已经成功运行的软件系统，我们在设计新的软件系统时，不可能完全放弃原有的软件系统。

但是经常遇到的情况是原有的软件系统和新的软件系统具有不同的理念，在考虑到扩展性的同时，必须兼容原有的软件系统，此时适配器模式是我们首选的设计模式。

我们看一下适配器模式的定义：适配器模式将一个类的接口转换成客户希望的另外一个类的接口。

适配器模式使原本不兼容而不能一起工作的类可以一起工作。

适配器模式并非特别的技术，其实质是在新的类中借用(翻译）原有类的动作和行为。

在面向对象的编程中，当然是两个类乊间的关系。

对于LV来说，由于早期不存在LVOOP，因此适配器很少针对两个类，但是适配器模式的设计思想完全可以推广到面向过程和面向对象的混合编程中。

下面我们通过一个绘图类说明如何使用适配器模式。

我们的目的是建立一套通用绘图程序类，包括点、线、圆等等，仍图形的角度看，无论是点还是圆形，都存在很多共同点，比如绘图颜色、画笔等等，因此建立一个形状的类作为基类是非常合适的，在基类的私有数据中存储公共特征，比如颜色和画笔，另外需要在基类中创建一个可重写的绘图函数，这样基类和继承的特殊形状的子类都可以使用同一绘图函数，实现类的多态特性。

我们创建一个形状类作为基类，形状类的私有数据包括画笔和颜色，并分别创建了私有数据的读写属性，形状类中，我们创建了可重写的绘制形状方法。

属性的程序框图非常简单，就不贴图了。

看一下形状类中可重写绘制形状的程序框图。

在基类的绘图函数中，不执行任何实际绘图工作，具体绘图工作延迟到具体子类中实现。

我们知道，绘制一个圆需要圆的半径和圆心，其中圆心是一个点，因此我们创建一个点类，并将点类作为圆类的私有数据成员乊一。